In accordance with a rapid spread of information related devices and communication devices such as a personal computer, a video camera and a cellular phone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been under progress also in an automobile industry. Among various kinds of batteries, a lithium battery has been presently noticed from the viewpoint of having a high energy density.
Liquid electrolyte containing a flammable organic solvent is used for a presently commercialized lithium battery, so that the installation of a safety device for restraining temperature increase during a short circuit or the improvement in structure and material for preventing the short circuit is necessary therefor. In contrast, a lithium battery all-solidified by replacing the liquid electrolyte with a solid electrolyte layer has a simplified safety device and it is considered to be excellent in terms of production cost and productivity for the reason that the flammable organic solvent is not used in the battery. Furthermore, as a solid electrolyte material used for a solid electrolyte layer, a sulfide solid electrolyte material is known.
As the sulfide solid electrolyte material has high Li ion conductivity, it is useful for obtaining high output of a battery. Thus, various studies have been conventionally made. For example, in Patent Literature 1, it is disclosed that glass ceramics can be obtained by heat treatment of LiI—Li2S—P2S5-based sulfide glass. Further, in Patent Literature 2, it is disclosed that the Li ion conductivity can be improved by adding LiI, LiCl, LiBr, or the like to Li2S—P2S5-based sulfide solid electrolyte. Further, in Patent Literature 3, Li2S—P2S5—LiX—Li2CO3-based solid electrolyte is disclosed. Incidentally, X represents I, Cl, or Br. Still further, in Patent Literature 4, adding a plurality of LiI, LiCl, LiBr, or the like to Li3PO4—Li2S—P2S5-based solid electrolyte is disclosed.